The present invention relates to a multi-axes industrial processing machine, and more particularly to an industrial processing machine with multi-axle electrical drive systems that include built-in motors controlled by a centrally regulated supply module.
Multi-axes industrial processing machines include, among others, machine tools and production machines. Conventional in machine tools are, for example, lathes, milling machines, drills or winding machines. Machine tools also include central processing facilities, linear and rotary transfer machines, laser machines and/or rolling and gear cutting machines. These machines have in common that a material can be machined along multiple axes. Production machines can be used to process textiles, plastics, wood, glass, ceramics or rocks. Production machines can be employed in metalworking and/or packaging, printing and materials-handling.
Modern industrial processing machines are constructed with built-in motors, in particular linear motors and torque motors, eliminating mechanical components, such as gears, drive belts, and spindles. This reduces the size of industrial processing machines and increases productivity. A compact design can be achieved with built-in motors, because they can be better integrated in the mechanical configuration of the industrial processing machine than conventional motors. The electric motor together with the surrounding mechanical configuration forms a mechatronic unit.
However, in the event of a malfunction, built-in motors are difficult to access and hence more difficult to exchange. This makes the installation more expensive and can cause long machine downtimes. Built-in motors therefore must operate reliably over a long time.
A processing machine of this type includes a multi-axes converter system that drive several built-in motors of the multi-axes industrial processing machine. The converter system in conjunction with the motors form of the multi-axle drive system. The multi-axes converter system is housed in a switchbox of the industrial processing machine and includes a centrally controlled supply module with a smoothing choke on the AC side and several axes modules. These modules are electrically connected on the DC side via a DC intermediate circuit. On the AC side, each axle module is electrically connected with a built-in motor, forming an axis drive. It is hereby inconsequential if the axle module and the associated built-in motor are implemented as separate units or not. The axle modules can be implemented as multi-phase free-running pulse converters using Insulated-Gate-Bipolar-Transistors (IGBT).
The centrally arranged regulated supply module with the smoothing choke on the AC side generates from a multi-phase line voltage a constant regulated DC voltage with an amplitude that is greater than the DC value of the line voltage on the input side. To generate this regulated DC voltage, the supply module cooperates with the smoothing choke to form a voltage up-converter. The centrally arranged regulated supply module together with the smoothing choke on the AC side forms a regulatable DC source.
In addition to these elements of the multi-axes converter system, parasitic capacitances to ground have to be taken into account. These so-called leakage capacitances form in conjunction with the inductance of the smoothing choke and the inductance of an additional line filter a weakly damped oscillator circuit. The switching processes of the central supply module as well as the switching processes in the various axes modules excite oscillations in the weakly damped oscillator circuit at its natural resonance frequency.
Due to resonance conditions, an objectionable resonance oscillation with an amplitude of up to several 100 V can be superimposed on the potentials of the DC intermediate circuit of the converter system. As a result, the intermediate circuit operates farther from its intrinsic symmetric rest position than when only the switching process of centrally arranged supply module is considered. The weak damping of the resonance circuit generates high peak voltages. An electric motor can thereby exhibit a frequency characteristic with a pronounced resonance overshoot against ground. This overshoot occurs in the region of the star point of the motor which is typically incapable of withstanding excessive voltages. If the system converter system oscillates close to a motor resonance frequency, then the isolation to ground, in particular at the star point, of each electrical machine of the multi-axle drive system can be overloaded and can cause a premature failure of individual motors of the multi-axle drive system, because the resonance can generate significantly higher voltages at the motor star point than at the motor terminals.
A premature failure of a motor of a multi-axes industrial processing machine with built-in motors could cause long machine downtimes and a significant loss in production due to the poor accessibility of the built-in motors.
German patent publication no. DE 100 59 334 A1 discloses measures for attenuating the afore-described resonance overshoots of an electric motor that is operated with a converter having a voltage intermediate circuit, by connecting an impedance between the star point of the motor and ground. This impedance, which advantageously includes a series connection of an ohmic resistor and a capacitance, attenuates the capacitive leakage currents to ground potential that are generated in the winding strands of the motor. This impedance is dimensioned so as to sustain the asymmetric leakage currents to ground caused by the system oscillations of the converter system produced by the motor phases.
A prerequisite for using these conventional measures is that the star point terminal of the motor is accessible from the outside, and the built-in motor leaves enough space for the impedance. In addition, this measure has to be applied to each motor of a multi-axle drive system.
German Patent publication no. DE 100 59 332 A1 discloses another measure for solving the afore-described problem. According to this measure, a magnetic core is provided, through which the phases of a motor are routed in common. This magnetic core has a winding, with an impedance connected in parallel with the winding, so that the impedance short-circuits the winding. This winding transformer-couples the impedance to all phases of a motor. Because all phases of a motor are routed through this magnetic core, only the interfering common-mode processes of the characteristic system oscillations of the converter system are attenuated.
This solution also requires that enough space is available for the transformer-coupling of the impedance to all phases of a motor in the drive system. The magnetic core with the short-circuited winding has to be placed between the output of an axle module and the terminal box of a corresponding motor. This measure also affects the damping of characteristic system oscillations of the converter system on a motor. In a multi-axle drive system magnetic, a number of cores with short-circuited windings that correspond to the number of axes have to be provided. This solution advantageously no longer requires the star point for the damping, which therefore no longer needs to be externally accessible.
German Patent publication no. DE 100 59 332 A1 discloses a motor for an industrial processing machine with an electric drive system, a supply module, a smoothing choke, an axis drive and an DC-equivalent source producing a DC voltage, wherein an impedance is transformer-coupled at the input of the motor, thereby preventing resonance overshoots excited by system oscillations.
It would therefore be desirable and advantageous to provide a multi-axes industrial processing machine, which obviates prior art shortcomings and is able to specifically dampen characteristic system oscillations for all axes in a cost-effective and space-saving manner.